Question:
Why is the citric acid cycle called an amphibolic pathway?
Why is the citric acid cycle called an amphibolic pathway?
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Amphibolic means it bridges catabolism and anabolism.
Updated On: Jun 24, 2026
- Both exergonic and endergonic reactions take place
- Metabolites are utilized in other pathways
- It can proceed both in forward and backward direction
- Same enzymes can be used in reverse directions
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The Correct Option is A
Solution and Explanation
Step 1: The term amphibolic means a pathway that serves both catabolism and anabolism. The citric acid cycle qualifies because it links energy-yielding (catabolic) breakdown with energy-requiring (anabolic) biosynthesis.
Step 2: Catabolic reactions are exergonic (exothermic, energy releasing) while anabolic reactions are endergonic (endothermic, energy requiring). Because the cycle bridges these two, it carries both exergonic and endergonic reactions, which is the defining reason for the amphibolic label. Hence option 1 is correct.
Step 3: Option 2 states that intermediates feed other pathways, which is true but describes the anaplerotic and cataplerotic role rather than the strict meaning of amphibolic, so it is a weaker answer.
Step 4: Options 3 and 4 are incorrect: the cycle runs essentially in one oxidative direction in vivo, and reversibility of individual enzymes is not what amphibolic refers to.
Step 2: Catabolic reactions are exergonic (exothermic, energy releasing) while anabolic reactions are endergonic (endothermic, energy requiring). Because the cycle bridges these two, it carries both exergonic and endergonic reactions, which is the defining reason for the amphibolic label. Hence option 1 is correct.
Step 3: Option 2 states that intermediates feed other pathways, which is true but describes the anaplerotic and cataplerotic role rather than the strict meaning of amphibolic, so it is a weaker answer.
Step 4: Options 3 and 4 are incorrect: the cycle runs essentially in one oxidative direction in vivo, and reversibility of individual enzymes is not what amphibolic refers to.
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